iPhone X battery stuck after I removed battery flexble

Recently, I tried to repair iPhone X more than five devices

and every time I finished repairing, battery has problem.

Battery symbol won’t go up but after rebooting

battery jump up instantly.

So I tried to refrain battery using all night

then the problem has solved.

I tested empty battery for iPhone X

screen symbol said that charging

but never started.

So I have hypothesis

battery IC should get used to logic board

Thats why empty battery has never started

If you guys have answers please help me

and sorry for my bad English